An experimental study of vascular dynamics by an acceleration plethysmogram using artificial circulation devices

Plethysmogram has been widely known as a conventional non-invasive simple method to obtain information on peripheral circulatory kinetics. We made a quantitative assessment of the relationships between the various circulatory parameters, using the simple conventional measurement method of treating acceleration plethysmograms (the second derivatives of digital plethysmograms) as indicators of peripheral circulation kinetics. We designed a prototype model peripheral circulatory circuit, using an artificial heart, for the purpose of clarifying the relationship between physical factors and plethysmograms. In our models of the peripheral circulatory system, we made use of various types of matching silicon tubes, as well as canine carotid arteries, as substitutes for human arteries. We evaluated the mechanical characteristics, such as the pressure and volume characteristics of the silicon tubes and canine carotid arteries. Plethysmogram alterations were measured using a photoelectric digital plethysmogram. When we examined the acceleration plethysmogram b/a values, which indicate blood vessel extensibility and hardness, and the d/a values, which we were able to use as an index of peripheral circulatory kinetics, it was clear from out model testing that canine carotid arteries displayed b/a values that were closest to those found in the human fingertip; among artificial tubes, the closest was a tube with a diameter of 4 mm (0.18 mm in thickness). The b/a values of all types of tubes declined when the compliance of the arterial system was increased, and it was confirmed through model testing that b/a values are an indicator of blood vessel extensibility.